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Dear Greg, On Jan 31, 2008 8:43 PM, Greg ----- <[log in to unmask]> wrote: > Is it feasible to use fsl's cluster thresholding alongside fdr to look for > regions of activation or is this considered "fishing for result" per se? > FDR aside, doing both cluster- and voxel-wise inference isn't "fishing" per se, but it will result in inflated false positive rates. Hence, once has to commit to a single inference strategy before seeing the data to be sure you can trust your P-values. To be clear, cluster inference in FSL always uses a familywise error (FWE) correction--a 0.05-corrected significant cluster controls the chance of 1 or more false positive clusters anywhere in the brain. Similarly, the standard FSL voxel-wise corrected significance controls for the chance of 1 or more false postive *voxels* anywhere in the brain. FDR is only available for voxel-wise inference (it has been proposed for cluster inference, but FDR works best with many many tests and sparse signals, and there just aren't that many clusters in a typical image). Hence your question suggested a combination of FWE cluster-wise inference and voxel-wise FDR inference, which isn't so much apples and oranges, as apples and turnips. Hope this helps! -Tom ____________________________________________ Thomas Nichols, PhD Director, Modelling & Genetics GlaxoSmithKline Clinical Imaging Centre Senior Research Fellow Oxford University FMRIB Centre